Partitioned impact absorbers are already known, being honeycomb-type structures comprising an array of partitions extending parallel to a predetermined "impact" direction, and which deform in the event of an impact, thereby absorbing the energy thereof.
By way of example, such impact absorbers are used for mounting bumper beams to vehicle structures or they are mounted directly to the structure of the vehicle. When the impact absorber is subjected to an impact directed substantially along the axis of the vehicle, the bumper beam moves towards the inside of the vehicle and the energy transmitted by the bumper beam is absorbed by the impact absorbers so as to protect the remainder of the vehicle and above all its passengers.
Until now, partitioned impact absorbers have generally been obtained by extrusion or by injection.
When obtained by injection, there is a lower limit on the pitch of the array of partitions, i.e. on the distance between two adjacent partitions in the array, because the injection mold and in particular the cores which separate the partitions, must present at least some minimum thickness below which they would not withstand the very high injection pressure that needs to be exerted in order to fill completely the cavities in the mold between the cores and defining the volume in which said partitions are made.
With injection, the pitch of the array must also be larger with increasing depth of the partitions in the impact direction. Unfortunately, this correlation between partition depth and array pitch as imposed by the injection process is particularly unfavorable to the effectiveness of the absorber.
Ideally, in order to be effective during a high-energy impact, the depth of the partitions should be large and simultaneously the size of the cells, i.e. the pitch of the array, should be small.
In addition, there is another characteristic of injected absorbers that reduces their effectiveness: the fact that the partitions must be of tapering thickness towards the ends of the cores so as to enable the absorber to be unmolded. The consequence of this characteristic is that the resistance opposed by the absorber increases with increasing depth of compression, which phenomenon is referred to as the taper phenomenon, whereas more energy would be absorbed if the resistance opposed by the absorber was at its maximum from the beginning of its deformation.
As a result, previous molded impact absorbers provide energy absorption conditions that are not satisfactory because of the relatively low density of their arrays of partitions and because their efficiency is diminished by the taper effect.